1. Field of the Invention
The invention relates in general to electrical apparatus and, more particularly, to circuit breakers including means for automatically separating the contacts upon occurrence of an overcurrent condition.
2. Description of the Prior Art
Circuit breakers generally employ a pair of separable contacts connected to an operating mechanism to open and close the contacts in response to manual operation of an operating handle between opened and closed positions. In addition, circuit breakers include means for automatically separating the contacts upon occurrence of an overcurrent condition. This automatic operation is carried out by the of a toggle linkage connected to a movable contact arm, a latched cradle, and an operating spring. Upon occurrence of an overcurrent condition, a latch is operated to release the cradle and cause the line of action of the operating spring to move such as to produce a collapse of the toggle linkage. The contact arm is then rotated by the operating spring until restrained by a fixed arm stop. Contact separation and circuit interruption are thereby produced.
In a circuit breaker constructed in this manner, the distance of maximum contact separation determines the breaker performance, according to such criteria as maximum interrupting capacity and voltage rating. In order to increase the operating performance, the maximum contact separation must also be increased by changing the position of the arm stop. This, in turn, requires an increase in the strength of the operating spring or an increase in the arc of operation of the handle. These modifications are often not practical, due to size constraints of the breaker housing. It would, therefore, be desirable to provide a circuit breaker having an increased contact separation distance during automatic interruption without the necessity for increasing the operating spring force or the required operating arc of the operating handle.